The present invention relates to such a method of assembling a piston ring as is applied to the assembling of a thin piston ring, and to a method of assembling a set oil ring comprising a spacer ring and a pair of side rail rings into a piston ring groove of a piston, as well as to an apparatus for assembling a set oil ring.
Conventionally, in assembling the set oil ring, the spacer ring is first assembled into the piston ring groove and then each side rail ring is assembled into each groove portion to be formed between the spacer ring and the upper groove surface and the lower groove surface, respectively, of the piston ring groove.
The assembling of this kind of spacer ring and the side rail rings is conventionally carried out, as disclosed in Japanese Published Examined Patent Application No. 2020/1983 and Japanese Published Examined Patent Application No. 19376/1986, Japanese Published Examined Utility Model Registration Application No. 16020/1986, and others, by positioning or aligning, relative to the piston, a guide member having a larger diameter than the outside diameter of the piston, and then pushing the rings mounted on the external periphery of the guide member out of the front end thereof. As the guide member, there are provided three kinds for the spacer ring, the upper-side side rail ring and the lower-side side rail ring. A corresponding guide member is thus used in each of the different assembling stations to independently assemble the spacer ring and the upper-side side rail ring and the lower-side side rail ring.
For example, in assembling the lower-side side rail ring into the groove portion between the spacer ring and the lower-side groove surface, there will be used a guide member whose lower end coincides with the upper surface level of the groove portion. There will then be disposed, under the guide member, a restricting member which faces the guide member with a clearance which is slightly larger than the thickness of the side rail ring. The side rail ring which is mounted on a periphery or external surface of the guide member is pushed out of the lower end of the guide member to thereby assemble the side rail ring into the groove portion through the clearance between the guide member and the restricting member.
Such a thin ring as the side rail ring has a smaller rigidity in the direction of its thickness and, therefore, it is likely to be bent to form undulations in the direction of its thickness when it is expanded in diameter by inserting it into the external surface of the guide member. As a solution, in the above-described prior art, a restricting member is oppositely disposed under the guide member, and the clearance between the two members is set to a size which is equal to the thickness of the side rail ring added by a small clearance to allow for the side rail ring to pass therethrough. It is thus so arranged that the undulations of the side rail ring are corrected while it passes through this clearance.
In this method, however, it is necessary to strictly control the amount of the clearance between the guide member and the restricting member in accordance with the thickness of the side rail ring, as well as to strictly control the relationship of the clearance to the piston so that the clearance is in right opposite the ring assembling position of the piston. As a result, due to high requirements of accuracy of positioning the guide member relative to the piston, the equipment becomes complicated and expensive.